Cylinder locks and respective keys are known whose characteristics are described in EP1121502 (priority, Italian application no. B098A000586 filed on Oct. 15, 1998) in the name of this same Applicant. This document describes a cylinder lock whose code cannot be deciphered immediately from the outside, so as to hinder tampering therewith.
This result is obtained by arranging at least one tumbler at right angles to the keyway in the plug of the cylinder, said tumbler having a respective end that protrudes into said keyway.
The tumbler is associated with respective complementary tumblers that can translate elastically from a configuration in which they are fully accommodated within the plug to at least one configuration for simultaneous accommodation in the body and in the plug, with consequent coupling of these two parts.
The key has a movable pad, which is forced elastically into conditions of substantially co-planar arrangement with a respective surface of the key and is accommodated so that it can slide within a respective seat.
When the key is inserted in the keyway, it actuates the tumblers, arranging them so that the complementary tumblers are in the configuration in which they are fully accommodated within the body, allowing any movement of the plug following a rotation of said key.
The presence of the movable pad in the key, associated with the at least one tumbler, ensures higher security of the lock with respect to break-in actions generically known as picking (mechanical tampering).
The tumbler that acts on the movable pad is in fact constituted by an actual tumbler provided with an end stem, which engages in a complementary tumbler provided with a cavity whose shape and dimensions are complementary to those of the stem. Appropriate elastic means are arranged between the tumbler and the complementary tumbler and are intended to keep them at the maximum mutual distance.
When the lower end of the tumbler abuts against the movable pad, a compression of the elastic element arranged between the movable pad and its seat in the key is induced. The elastic action of the elastic element controlled by the pad is stronger than that of the elastic means interposed between the tumbler and the complementary tumbler, causing a compression thereof.
In practice, movement of the plug is possible only when the respective key is inserted correctly within the keyway of the lock, in order to release the at least one perpendicular tumbler provided with said elastic means.
Unfortunately, it has been observed that it is possible to break into this type of lock by using keys provided with holes at the seat that should accommodate the movable pad.
These holes can, for break-in purposes, be filled with elastically deformable material. The gradual insertion of said material into the hole, with consequent repeated attempts to open the lock, allows identifying the amount of elastically deformable material that is necessary to emulate the original key, making it possible to open the lock.